renderer_vulkan: Drop dependency on Vulkan-SDK

* Dynamically fetch vulkan function pointers and checkout Vulkan-Headers.
This way we are not tied by the installed SDK version

externals/CMakeLists.txt

@@ -132,6 +132,7 @@ if (ENABLE_WEB_SERVICE)
     SET(CPP_JWT_USE_VENDORED_NLOHMANN_JSON ON CACHE BOOL "Use included json-hpp")
     add_library(cpp-jwt INTERFACE)
     target_include_directories(cpp-jwt INTERFACE ./cpp-jwt/include)
+    target_compile_definitions(cpp-jwt INTERFACE CPP_JWT_USE_VENDORED_NLOHMANN_JSON)
 endif()
 
 # lodepng